ENVIRONMENTAL RELATIONS OF THE BRYOPHYTIC AND VASCULAR COMPONENTS OF A TALUS SLOPE PLANT COMMUNITY

The environmental factors correlating with community structure of vege tation on talus slopes of the 785 km long Niagara Escarpment, southern Ontario, Canada, were studied using canonical correspondence and regr ession analysis. The bryophytes and higher vascular plants were analys ed separately to see if their responses were similar or different. Bot h vascular plants and bryophytes responded similarly to the environmen tal variables that were measured. For both vegetation components, loca tion from north to south explained most of the variance. When species richness was plotted against location for the complete vegetation and for the two components separately, the results showed that vascular pl ant species richness decreased with increasing latitude, while bryophy te richness increased. The magnitude of both of these trends was sligh t but consistent with the hypothesis that available environmental ener gy governs a significant amount of the variance in species richness. S ince separate components of the talus vegetation were shown to respond differently to the same environmental variable, groups of taxa should not be excluded from community level studies without a consideration of the possible consequences of this bias.